1. Field of the Invention
The invention relates to a method and apparatus for identifying post consumer or post industrial waste carpet using an infrared (IR) spectrometer, and more particularly to a method of identifying post consumer or post industrial waste carpet using a hand-held IR spectrometer having an IR radiation source which illuminates the post consumer or post industrial waste carpet with IR radiation, a selector for selecting a predetermined number of discrete wavelengths of radiation and an IR detection system for detecting radiation reflected by the post consumer or post industrial waste carpet. The invention also relates to a method and apparatus for identifying Polyamide-6 and/or Polyamide-66 containing material using a hand-held IR-spectrometer enabling sorting of the Polyamides.
2. Description of the Related Art
Recycling post consumer or post industrial waste carpet material requires the post consumer or post industrial waste carpet material to be sorted according to the type of face fiber used to manufacture the carpet. Throughout this application, applicants will repeatedly refer to "post consumer waste carpet", which is used by applicants as a generic term encompassing both post consumer waste carpet, post industrial waste carpet and Polyamide-6 and/or Polyamide-66 containing waste streams.
Currently, carpets employ face fibers produced from materials such as Polyamide-6, Polyamide-66, Polypropylene, Wool, Polyester and blends of these component products. For a recycling program to be successful, it must be easy to accurately identify the type of face fiber used by the carpet.
One method of identifying carpets is to print a code on the back of the carpet. Unfortunately, although this is the most fool-proof of all possible methods, it requires the carpets to have been marked when manufactured. Therefore, even if marking was started today, this method would not become effective for approximately 10 years due to the expected life of the marked carpet. Further, this method may not be satisfactory when used with glued carpets, since the backing of glued carpets may be damaged, thus rendering the identification code difficult to read.
Alternatively, it is possible to identify the type of carpet by detecting the melting point of the face fiber. This identification method is inadequate because it is not able to separate streams of Polyester and Polyamide-66. Further, blends of the various types of face fibers cannot be distinguished. Devices which utilize the melting point of the carpet material as a distinguishing characteristic are also deficient in that they generally tend to have a long warm-up time, thus reducing efficiency, and can be dangerous since they necessarily involve hot components.
A third way to identify the type of face material used on a particular waste carpet sample is to use a spectroscope. It is well known that various materials can be identified using vibrational spectroscopic techniques like mid-infrared and near infrared spectroscopy. In particular, near infrared spectroscopy is a well known method, e.g. for the sorting of bottles. IR spectroscopy can be conducted on transparent materials by analyzing radiation passing through the materials, and on substances which are opaque to IR radiation by analyzing the diffuse radiation reflected by the material. To conform with the customary usage in optics, this application will sometimes refer to IR radiation as "light".
IR spectrometers, for both the near-infrared range (800-2500 mm) and the mid-infrared range (2500-25000 mm), are often used to identify and quantify materials on the basis of the material characteristics which cause them to absorb or reflect particular wavelengths. In many cases, these characteristic frequencies are only slightly different for different materials. It is therefore important to use a high spectral resolution spectrometer, especially when attempting to distinguish various materials mixed together.
An IR spectrometer generally includes a source which emits radiation in the desired wavelength range and auxiliary optics such as lenses and mirrors to form the radiation into a beam of suitable shape and dimensions and to guide it along a light path. As a rule, all elements that make up the spectrometer are accommodated in an enclosure which preferably is sealed to prevent dust from interfering with the components.
The light source is preferably placed in a reflector casing so that the spectrometer can obtain as much light as possible. The light source is preferably incorporated in the optical casing, so that light egresses from the spectrometer via an optically transparent window to impinge on the target material. The transparent window may be, for instance, glass or high-quality quartz or may be made of for instance KBr, KCl, ZnSe, KRS.sub.5, CaF.sub.2 or MgF.sub.2 for the mid-infrared range.
The beam is directed at a site on the material to be examined. The reflected radiation is then collected, formed to have a desired beam geometry and eventually directed onto a detection system. This detection system normally includes a detector capable of measuring the intensity of the incident radiation. Several detectors which may be used in the near-infrared range include PbS and InGaAs detectors, and detectors which may be used in the mid-infrared range include detectors made from deuterized triglycinesulphate (DTGS).
There are several basic types of IR spectrometers. Two types of IR spectrometers are discussed below. In the first type, discrete wavelengths are selected by passing reflected radiation through different filters that are only transparent to a particular wavelength range. In the second type, a beam of reflected IR radiation is dispersed and allowed to impinge on a diode array. Unfortunately, diode arrays of this nature and having the desired resolving power are very expensive, and selection of the desired wavelength from the absorbed spectrum must take place in a later phase in the downstream processing equipment, thus increasing the amount of support electronics necessary to utilize the spectrometer.
The relationship between the intensity and the wavelength of the reflected or transmitted light from a particular material is called the spectrum. The detector is linked to a processing system which converts the detector signals into a spectral form accessible to the user or a computer such as a curve or numerical values.
In general, the mid- and near-infrared spectra of various types of fibers used in carpets differ significantly. However, the spectra of polyamide-6 and polyamide-66 differ only slightly: the mid-infrared spectrum is completely identical and the near infrared spectra is only slightly different in the 2000-2500 nm spectral range.
The quality of identification obtainable using a given spectroscopic system is expressed as the Mahalonobis-distance (MD), which is the center-to-center distance between the various clusters in relation to the spread within the clusters. For good separation, a minimum MD value of about 6 is required, but ideally the value should be larger than 10.
Unfortunately, although Ghosh and Rogers (Melliand Textilberichte 5, 1988, pages 361-364) indicated that the scanning spectrometer in their system achieved very good MD results for sorting Polyamide-6 and Polyamide-66 fibers (MD=18), the size and price of the scanning spectrometer renders this system largely unsuitable for use in the carpet recycling business. Ghosh and Roogers also demonstrated that it is possible to identify nylon 6 and nylon 66 fibers used for carpet production using a Bran&Luebbe (Formerly Technicon) InfraAlyzer 500C, with a combination of 3 filters, (2250, 2270 and 2310 nm).
These reported results are also deceiving, in that used carpets have different fiber materials than new carpets due to wear and contamination, thus complicating identification. For example, using these same 3 filters on a sample of 113 post consumer carpet waste samples, applicants discovered that the obtainable MD ranged between 4, and 1.2, depending on the resolution of the spectrometer. As indicated above, results of this nature are clearly insufficient to accurately discriminate between various carpet samples. Accordingly, it still has not been demonstrated to be possible to distinguish various types of post consumer waste carpet utilizing a cheap, small and portable spectrometer based on selected wavelengths.
Likewise, although portable inexpensive IR filter-based spectrometers are commercially available for task specific applications, such as to determine the moisture content of various materials, no one has been able to develop a hand-held spectrometer which is able to satisfactorily distinguish between various types of carpet face material so that the spectrometer can be suitably used in recycling post consumer waste carpet.